The present invention relates to disc drive data storage systems. More particularly, the present invention relates to a disc drive suspension having a moving coil or moving magnet microactuator.
Disc drive data storage systems use rigid discs which are coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor which causes the discs to spin and the surfaces of the discs to pass under respective hydrodynamic (e.g. air) bearing disc head sliders. The sliders carry transducers which write information to and read information from the disc surfaces. Each slider is supported by a track accessing arm and a suspension. The track accessing arms move the sliders from track to track across the surfaces of the discs under control of electronic circuitry.
The suspension connects the track accessing arm to the slider. The suspension includes a load beam and a flexure. The load beam provides a preload force which forces the slider toward the disc surface. The preload force is generated by forming a preload bend in the load beam, which becomes elastically deformed when the track accessing arm, suspension and slider are loaded into the disc drive. The preload bend is typically positioned near the proximal end of the load beam, adjacent to the track accessing arm. The load beam has a comparatively rigid portion which transfers the preload force from the elastically deformed preload bend to the slider. The rigid portion is typically made by forming stiffening webs or flanges along the longitudinal edges of the load beam.
The flexure is typically a separate piece part that is welded to the load beam. The flexure is flexible in the slider pitch and roll directions to allow the slider to follow the disc topography. The separate flexure is usually formed from a thinner material than the load beam to increase its pitch and roll compliance. Alternatively, the load beam and the flexure may be formed of a single, continuous piece of material.
Microactuators are now being developed for finely adjusting the radial position of the slider relative to the disc surface. There are several types of microactuators, including piezoelectric microactuators and electromagnetic microactuators. In piezoelectric based microactuators, a piezoelectric crystal is mounted on a lever arm which also acts as an electrical ground terminal. The lever arm is formed on or welded to the load beam. This creates a direct path to the electrical ground plane of the suspension. The ground plane of the suspension becomes an active part of the piezoelectric voltage control loop. If the read/write transducers are also connected to the ground plane of the suspension, the control voltage for the piezoelectric crystal may interfere with the sensitive electrical features of transducers.
In some piezoelectric microactuators, the piezoelectric crystal is mounted in a plane perpendicular to the lateral plane of motion of the suspension. This out-of-plane position makes the piezoelectric crystal sensitive to lateral motions of the suspension, which can cause possible resonating of the piezoelectric crystal. This can turn the piezoelectric crystal into a noise generator in the transducer positioning control loop. Further, with piezoelectric microactuators, there is a constraining relationship between the natural resonant frequency of the piezoelectric crystal and the range of motion achieved by the microactuator. A shorter piezoelectric crystal has a higher natural frequency but a smaller range of motion. A longer piezoelectric crystal has a lower natural resonant frequency and a larger range of motion.
Piezoelectric crystals also have a relatively short working life, are susceptible to cracking and are sensitive to damage from assembly or over extension. A further difficulty with piezoelectric microactuators is that the piezoelectric crystals require a high voltage, in the range of 36-100 volts, which is normally not available in a disc drive.
Electromagnetic microactuators generate magnetic fields that, when placed close to the read/write transducers, can interfere with the magnetic fields used to read information from and write information to the disc surface. The magnetic fields generated by electromagnetic microactuators can also corrupt the data stored on the disc surface.
Improved microactuator structures are desired.